Salvage of catabolic products in ganglioside metabolism: a study on rat cerebellar granule cells in culture.

Cerebellar granule cells in culture were subjected to a pulse (0.5-4 h)-chase (0-4 h) of 10(-6) M [3H]ganglioside GM1 carrying the radioactive label at the level of NeuAc ([3H-NeuAc]GM1), Sph ([3H-Sph]GM1) or Gal ([3H-Gal]GM1) and the formed [3H]metabolites were determined. With all forms of [3H]GM1, there was formation of [3H]catabolites, including [3H]H2O and [3H]biosynthetic products obtained by recycling of [3H]NeuAc, [3H]Sph and [3H]Gal released during intralysosomal ganglioside degradation (salvage processes). Much higher amounts of [3H]H2O were produced from [3H-Gal]GM1 than [3H-Sph]GM1 and [3H-NeuAc]GM1; conversely, more products from salvage processes (polysialogangliosides GD1a, GD1b, GT1b, O-acetylated GT1b, protein-bound radioactivity) were obtained with [3H-NeuAc]GM1 than the two other forms of [3H]GM1. Liberated [3H]NeuAc produced 10-fold less tritiated water and 10-fold higher salvage products than [3H]Gal. Using [3H-NeuAc]GM1, granule cells appeared to metabolize 7.7% of membrane-incorporated exogenous GM1 per hour with a high degree of NeuAc recycling and the calculated metabolic half-life was 6.5 h.